The present invention relates to a high-pressure pumps with an on-off valve for feeding fuel to an internal combustion engine, particularly a vehicle engine.
Various types of high-pressure fuel feed pumps are known, and which are generally supplied with fuel from a normal tank by a low-pressure pump powered by an electric motor. The high-pressure pump normally comprises an on-off valve, which is opened automatically by the fuel fed to it by the low-pressure pump.
The body of known high-pressure pumps encloses at least a fuel compression chamber, and an actuating chamber housing pump actuating members; and the on-off valve comprises a shutter designed to ensure fuel flow to the actuating chamber, even when the valve is closed, to lubricate and cool the actuating members.
In one known radial-piston pump in particular, the pumps body houses three cylinders, in which slide respective pistons activated by a common cam carried by a shaft activated by the drive shaft; the cam is housed inside the actuating chamber or case of the pump; and the shutter is in the form of a hollow cylinder and slides along the wall of a radial hole in the pump body.
The pump body also has a fuel feed conduit for feeding fuel from the radial hole to the cylinders; the feed conduit is closed by the lateral wall of the shutter; and, to lubricate and cool the pump shaft, the cam, and the various pump body and piston friction surfaces, the shutter also has a calibrated axial hole permitting continuous fuel flow to the case.
To prevent fuel accumulating in an engine cylinder, in the event the respective injector breaks down, or to prevent fuel from being drawn from the actuating chamber in the event of poor or no supply by the low-pressure punts e.g. due to a fault, the shutter is closed automatically by a compression spring when the pressure of the incoming fuel falls below a given value.
The compression spring is housed inside the shutter and rests on a perforated plate, which has a surface for receiving the end of the spring and is normally fixed, e.g. welded, to the opposite end of the guide hole of the shutter.
In this known type of pump, machining the radial hole in the pump body, fixing the plate, and assembling the spring are difficult, high-cost operations involving considerable time and highly skilled personnel. Moreover, the perforated plate at the end of the hole facing the case limits to a certain extent the outside diameter of the cam and, hence, the capacity of the pump under given conditions.
It is an object of the invention to provide an extremely straightforward, reliable high-pressure pump having an on-off valve which is cheap to produce and easy to assemble, so as to eliminate the aforementioned drawbacks of known pumps with on-off valves.
According to the present invention, there is provided a high-pressure pump with an on-off valve for feeding fuel to an internal combustion engine, wherein the pump comprises a body including at least a fuel compression chamber and an actuating chamber enclosing actuating members of said pump, and wherein said valve comprises a shutter sliding inside a hole in said body to close a fuel feed conduit; said feed conduit being formed in said body, between said hole and said compression chamber; and said shutter being held in the closed position by a compression spring; characterized in that said spring rests directly or indirectly on a shoulder inside said hole; said shoulder being formed in one piece with said body.
In a first embodiment of the invention, the spring rests on the shoulder by virtue of means fixed removably inside the hole and comprising a perforated disk inserted removably inside the hole, and an elastic C-shaped metal element located, between the disk and the shoulder, inside an annular groove adjacent to the shoulder.
In a further embodiment of the invention, the spring rests directly on the shoulder, and the wall of the hole has an annular groove permitting precision machining of the wall.